System and stent for repairing endovascular defects and methods of use

ABSTRACT

Disclosed are endovascular stents in which a portion of the stents have a bioactive coating for promoting repair of damaged vessels, systems comprising the stents, and methods of using the stents to promote occlusion of aneurysms and/or repair damaged vessels.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority to U.S. Provisional Application No.61/544,104, filed Oct. 6, 2011, which is incorporated by reference inits entirety.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

This invention was made with government support under Grant No.W81XWH-11-2-0067 awarded by the U.S. Department of Defense. The UnitedStates Government has certain rights in this invention.

FIELD OF THE INVENTION

The invention relates generally to a system, vascular stents and methodsof repairing endovascular defects. More particularly, the presentinvention relates to a system, vascular stents, and methods for treatinginjured or defective blood vessels, including aneurysms, such asneurovascular aneurysms. The vascular stent employed in the system andmethods of the invention includes a bioactive coating for use intreatment of injured or defective blood vessels, including intracranialor cerebral aneurysms.

BACKGROUND OF THE INVENTION

An aneurysm is an abnormal bulging or ballooning of an artery due to aweakness in the arterial wall. Intracranial or cerebral aneurysms, whichoccur in approximately 2% of the population, are frequentlylife-threatening when rupture occurs. Conventional treatment includessurgical clipping to bypass the aneurysm and endovascular coiling of theaneurysm. Endovascular coiling involves packing the aneurysm with smallplatinum coils to cause embolization of the aneurysm. Endovascularcoiling has the advantage of being less invasive than surgical repair ofintracranial aneurysms, because the coils are delivered by a catheterinserted into a femoral artery of the patient.

Although endovascular coiling has been effective in the treatment ofnarrow neck aneurysms, it is less effective in treating wide neckaneurysms. The irregular interface between the coil mass and the parentartery increases the risk of thrombosis leading to stroke, especially inwide neck aneurysms. Further, because filling the aneurysm sac withcoils does not address the diseased parent artery segment, there remainsa high risk of regional recurrence of an aneurysm. Stents have been usedin stent-assisted coiling in the treatment of patients with wide-neckedintracranial aneurysms to maintain the coils in place and to maintainthe patency of the affected artery. However, stent-assisted coiling inthe treatment of wide neck aneurysms is problematic due to challengesassociated with the anatomical reconstruction of a large segmentalparent artery defect and impaired durability of the affected vessel.

Ionita et al. described the use of a variable porosity stent with a lowporosity patch that covers the aneurysm neck as a primary treatment ofintracranial aneurysms (Ionita et al., 2009 Stroke 40:959-965). Thevariable porosity stents of Ionita, referred to as asymmetric vascularstents (AVS), were used to treat aneurysms in rabbits. Each of the ninerabbits treated with AVS showed complete occlusion of the aneurysm;however, three of the nine rabbits died subsequent to AVS treatment.

There is a need in the art for systems, stents, and methods of treatinganeurysms that reduce inflow of blood from the aneurysm to the parentartery while minimizing risk of thrombogenic occlusion of the parentartery and/or heal the damaged vessel. The present invention satisfiesthat demand.

SUMMARY OF THE INVENTION

In one embodiment, the present invention includes an endovascular stentfor use in repairing an injured, damaged, or defective blood vessel. Thestent has the advantage of being suitable for occluding aneurysms and/orrepairing damaged vessels.

The stent may be delivered to the site of the vessel in need oftreatment by catheterization, e.g., via the femoral artery. Thus, in thetreatment of intracranial vessel damage, e.g., cerebral aneurysms, thestents and methods of treatment using those stents, are minimallyinvasive compared to surgical methods of repair.

The stent of the invention is designed to have a coating on a portion ofthe stent surface. The coating includes a magnetic material deposited onportion of an outer surface of the stent, an ion-beam nanostructuredbiocompatible layer, and a bioactive layer formed on the biocompatiblelayer. The bioactive layer comprises PCSM.

In certain embodiments, the stent includes an underlayer between thestent surface and the magnetic layer in order to promote better adhesionof top layers.

Advantageously, the magnetic region may be made of any suitablematerial, including a metal layer, or a biopolymer impregnated with amagnetic metal.

In certain embodiments, the stents may also include nanoscale particlesimbedded in the coating to facilitate radiation-enhanced tomography.

The stents were designed for treatment of intracranial aneurysms, inparticular wide neck aneurysms.

In another embodiment is provided a system for delivering a stent to a

-   -   a cerebral artery comprising an endovascular catheter, the stent        of the invention, and magnetized cells. Interaction of the        magnetized cells with the magnetized coating directs cells that        promote healing and regrowth of damaged vessels to a targeted        region.

In another embodiment are provided methods of repairing a cerebralartery and/or occluding an aneurysm by delivering the stent of theinvention to the cerebral artery comprising the aneurysm, such that theportion of the stent comprising the coating is proximal to the neck ofthe aneurysm.

The present invention and its attributes and advantages will be furtherunderstood and appreciated with reference to the detailed descriptionbelow of presently contemplated embodiments, taken in conjunction withthe accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The preferred embodiments of the invention will be described inconjunction with the appended drawings provided to illustrate and not tolimit the invention, where like designations denote like elements, andin which:

FIG. 1A shows a cross-section of an embodiment of a stent having abioactive coating on an abluminal surface of the stent.

FIG. 1B depicts a vessel with an aneurysm containing a stent having abioactive coating the abluminal surface facing the aneurysm.

FIG. 2 illustrates an embodiment of the stent bioactive coating of FIG.1.

DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION

The embodiments disclosed below are not intended to be exhaustive orlimit the disclosure to the precise forms disclosed in the followingdetailed description. Rather, the embodiments are chosen and describedso that others skilled in the art may utilize their teachings.

In one embodiment, the present invention provides stents for use in thetreatment of intracranial or cerebral aneurysms. A portion of the stentdesigned for placement proximal to the neck of the aneurysm comprises abioactive stent coating. The bioactive stent coating includes a magneticportion for attracting magnetized cells.

This disclosure includes a minimally invasive protocol for treatment ofcerebral aneurysms. Endovascular surgical treatment makes use of acatheter-based stent deployment to the patient. A bioactive stentcoating prototype therefore is used that combines magnetic protocol forcell attraction with surface ion-beam driven nanopatterning for cellregulation at the molecular and cellular scale.

This protocol would allow for a fast endovascular treatment, minimizingcerebral trauma and prompt reconstructing of the aneurysmal neck defect.Reconstruction of the aneurysmal neck defect requires control of cellfunction at the molecular level.

This is the first technique to exploit nanoscale (10⁻⁹ m) to mesoscaletopography and control to regrow tissue at the neck orifice of acerebral aneurysm. Mesoscale is general defined as of intermediate size.For this disclosure mesoscale generally refers to length scales fromnanoscale to approximately microscale (10⁻⁷ m). In particular thistreatment seeks to exploit bioactive coatings that attract cells to thatregion asymmetrically and promote tissue growth by manipulatingnanopatterned surface on the coating.

In certain embodiments, a partially coated or asymmetrically coatedstent according to the present disclosure includes a region renderedmagnetic to locally attract biological cells, the magnetic regioncoupled with ion-beam nano-structured bio-compatible coating for tissueproliferation thus promoting healing, and use of porcine coronary smoothmuscle (PCSM) as nidus or locus for cell recognition, for effectivemembrane repair, expeditious endothelialization and enhanced durabilityin a pulsating blood environment, for example, near the aneurysmal neckregion. By combining a biocompatible multi-functional stent coatingfacing the aneurysmal neck defect, attraction of magnetic or magnetizedcells can be locally manipulated and rapidly promote tissue growthreconstructing the absent tunica media.

One embodiment of the invention is depicted in FIG. 1A, which shows across section of a stent portion 100 having a bioactive stent coatingaccording to the present invention. A stent wall surface 110 is coatedwith a nickel layer 120, having a gold layer 130 nanopatterned over thenickel layer 120, facing the abluminal side 160. The uncoated side ofthe stent wall 110 faces the luminal side 170. A plurality of magnetizedendothelial cells 150, such as HUVEC cells is proximal to the abluminalside 160 of the stent portion 100. The stent portion 100 of the stent ispositioned such that the portion having the bioactive stent coating 100is facing the neck of the aneurysm. In certain embodiments, the stenthas variable porosity, with a less porous portion that is positionedover the aneurysm neck region to induce stasis and subsequent thrombosiswithin the aneurysm. In general, the bioactive coating is fabricatedasymmetrically over only the portion of the stent that will span facethe aneurysm neck region, facing the aneurysm. The purpose for theasymmetric coating design is to confine the induced thrombogenicactivity to the aneurysm.

FIG. 1B illustrates a vessel 220 having an aneurysm 210 with a stent 230placed in the lumen of the vessel 220. The stent 230 includes a stentportion 100 as described above. The stent 230 is positioned within thevessel 220 so that the stent portion 100 is proximal to the neck regionof the aneurysm 210. The porosity of the stent portion 100 is lower thanthe porosity of the remainder of the stent 230.

With reference to FIG. 2, in certain embodiments, a stent according tothe present invention includes a stent portion 100 in which the stentwall surface 110, which is made of a material such as titanium, Nitinol,or SS316, comprises an underlayer 140 to support adherence of top layersto the stent surface. The underlayer is made of a material such as Cr. Alayer 120 such as nickel, rendered magnetic to locally attractbiological cells, overlays the underlayer. The magnetic layer 120 iscoupled to a bio-compatible coating 180 which includes an ion-beamnano-structured coating 130 made from a material such as gold and abioactive layer 190. The ion-beam nano-structured coating 130 includesnanostructures such as nano islands 200. The bioactive layer 190includes PCSM. The bio-compatible coating aids in tissue proliferationto promote healing, and PCSM functions as nidus for cell recognition.

Any stent suitable for vascular repair may be used in the stents andmethods of the invention. Examples of suitable stents include, withoutlimitation, titanium stents, Nitinol stents, and SS316 stents. A regionof the stent is rendered magnetic to locally attract biological cells.In certain embodiments, this is accomplished by coating a magnetic filmon the stent in the portion that will face the aneurysm neck regionusing electroplating. In certain embodiments, the magnetic film has athickness in the range of about 0.5-μm to about 10-μm. An underlayer(e.g. Cr) is deposited to adhere the top layers to the stent surfacematerial (e.g., Ti, Nitinol or SS316) using magnetron sputtering. Inanother embodiment, the stent may be rendered magnetic using magneticbacterial nanocellulose (MBNC), a unique biopolymer, which can be usedas scaffold for initial endothelial cell attraction and attachment.Bacterial nanocellulose (BNC) can be made magnetic by impregnation ofcandidate magnetic nanoparticles. Magnetic nanoparticles includingcobalt-ferrite and ferrite complex nanoparticles were synthesized andused to impregnate the BNC matrix to form MBNC. The MBNC was evaluatedfor the ability to attract magnetically loaded endothelial cells in asimulated vascular environment using a custom designed microfluidic flowdevice.

The matrix of BNC material can be loaded with various nanoparticles likesilver, ferric complexes, cobalt ferrite nanoparticles and organicmoieties. Triplets of BNC pellicles were grown at various pH conditions.It was found that pH 5 yields the optimal result. The magneticproperties of the MBNC have been established. The MBNC will be coupledto stents. Initial BNC films were prepared by culturing the bacterialstrain Glucanocetobacter xylinus (Cat. #53524, ATCC, Manassas, Va.) asfollows. A primary culture was formed by inoculating sterile Hestrin andSchramm media (containing D-glucose, 2.0% w/v, peptone, 0.5% (w/v);yeast extract, 0.5% (w/v), disodium phosphate, 0.27% (w/v), citric acid,0.115% (w/v), (pH 5.0). The bacteria was first inoculated (primaryinoculation, before homogenization) in the Hestrin-Schramm media andused for primary inoculation with solid agar. The culture was incubatedat 30° C. for 3 days in an incubator maintained at specific oxygen andmoisture content. Pellicles were formed at the interface of air/culturemedium and were harvested on day three. The leathery pellicles wereremoved and treated with 1 N NaOH solution at 75° C. for 20 minutes. Thepellicles were rinsed with Millipore water three times to remove theresidual bacteria. The purified BNC pellicles were freeze-dried beforefurther magnetic functionalization. The stents of the invention aredelivered to the aneurysmal neck defect by catheterization. Stentimplantation alters the hemodynamic flow behavior near the aneurysm neckorifice, thus leading to occlusion of the aneurysm. Catheterization willbe used to deliver nidus cells directly to the aneurysm neck orifice,with the cells attracted to the magnetic stent region. The velocityprofile and flow domain of the blood flow changes significantly aroundthe aneurysm neck orifice due to the aneurysm and implantation of thestent. This modified flow pattern has been well studied. It has beenreported that that implantation of stents reduces the intra-aneurysmalflow velocity of middle cerebral artery (MCA) aneurysms by about 43-64%affecting flow structure in the domes. The primary cause for thesechanges is the increased resistance to flow though the stent pores intothe aneurysmal sac. The delivery of cells by catheterization, reductionof flow velocity, and the vortex around the stent result in a decreasein drag force acting on the endothelial cells and as a result, amagnetic coating having a thickness of several micrometers coating issufficient to attract cells to the stent surface.

The cells can be magnetically labeled or magnetized using commerciallyavailable superparamagnetic iron oxide nanoparticles (MNP). Quantum dots(QDs) be used to label micelles. In certain embodiments, endothelialcell lines available commercially may be magnetically labeled for use inthe methods of the invention. In certain embodiments, the cells mayinclude Human Aortic Endothelial Cells (HAEC) or Human Umbilical VeinEndothelial Cells (HUVEC) (Invitrogen, Carlsbad, Calif.). Iron oxide(IO) nanoparticles are suited for biological testing because they have along blood retention time, and are therefore good for MRI contrast, theyare biodegradable, and they exhibit low toxicity. Briefly, cells may belabeled with IO nanocrystals (Ocean NanoTech, Springdale, Ak.) byincubating the nanocrystals with the cells for 2-3 h at 37° C. andallowing the cells to internalize the particles. Once the cells take upthe IO particles and become magnetic, the cells are washed to removefree nanoparticles and Transmission Electron Microscopy (TEM) can beused to verify particle internalization. Magnetically labeled cells maybe used immediately. Additionally, the IO nanoparticles may include astreptavidin tag that allows detection by a biotin-conjugatedfluorescent antibody and separation by cell sorting. Binding pairs otherthan streptavidin and biotin may be substituted.

Nanostructured surfaces of biomaterials have shown to stimulateadhesion, differentiation and proliferation on a variety of human stemcells. Our results have shown that Directed Irradiation Synthesis (DIS)can mimic the nano-scale environment influencing human umbilical veinendothelial cells (HUVEC-CS). HUVEC-CS were grown on silicon (Si) wafersdeposited with thin gold (Au) and palladium (Pd) films with a high cellproliferation rate and formed cell monolayers over the test materialsurfaces. A comparison of the toxicity and rate of DNA damage to cellsgrown on Au and Pd films magnetron-sputter deposited onto Si wafers tothat of experimental controls showed that the Au and Pd films have lowtoxicity and a low incidence of DNA damage. In contrast, HUVEC-CStreated with hydrogen peroxide exhibited toxicity and DNA damage thatwas significantly higher than that of HUVEC-CS seeded on knownbiocompatible materials (PDMS, Dermafill) and Au/Si—Pd/Si wafers.

In certain embodiments, a stent of the invention may include an ion-beamnano-structured bio-compatible coating suitable for tissue proliferationto promote healing. This may be accomplished by nano-topographyevolution of 100-200 nm thick gold film during irradiation by heavy-ionsputtering (e.g. Ar, Xe, etc.).

A tissue nidus is useful to repair a vascular defect across a scaffold.In vasculogenesis, there can be seen both spontaneous healing of a tinypuncture wound in arterial walls and failed vascular remodeling seen inaneurysms. To induce repair and reestablish the tunica media, anintervening homograft or allograft would be needed over the defect whichwould serve as the nidus to which the peripheral rim of the defect(aneurysm neck orifice) could direct its growth.

The PCSM was chosen as the nidus because PCSM cells can retain theirphenotypic plasticity in culture and thus mimic in vitro their in vivodifferentiation states as shown by various vascular studies.

Additionally, the arterial wall provides a source of stem cellderivatives for tunica media reconstruction. The nanostructured surfacesof the stent coating will act as a cue to guide the differentiation andproliferation of the internal stem cells.

The described embodiments above are to be considered in all respectsonly as illustrative and not restrictive, and the scope of the inventionis not limited to the foregoing description. Those of skill in the artwill recognize changes, substitutions and other modifications that willnonetheless come within the scope of the invention and range of theclaims.

Each cited reference is incorporated by reference in its entirety.

What is claimed is:
 1. A stent comprising a coating on a portion of itssurface for use in the treatment of a cerebral aneurysm, the coatingcomprising: a magnetic material deposited on portion of an outer surfaceof the stent; an ion-beam nanostructured biocompatible layer; and abioactive layer formed on the biocompatible layer, the bioactive layercomprising PCSM.
 2. The stent of claim 2, further comprising anunderlayer between the outer surface of the stent and the magneticmaterial.
 3. The stent of any one of claim 1 or 2, wherein the magneticmaterial is selected from a magnetic metal layer and a polymerimpregnated with a magnetic metal.
 4. The stent of claim 4, wherein themetal is nickel.
 5. The stent of claim 4, wherein the polymer isbacterial nanocellulose.
 6. The stent of any of claims 1-5, furthercomprising nanoscale particles embedded in the coating to provideradiation-enhanced tomography for visualization of the stent surface. 7.A system for delivering a stent to a cerebral artery having an aneurysmcomprising an endovascular catheter and the stent of any one of claims1-6.
 8. The system of claim 7, further comprising magnetized cells. 9.The system of claim 8, wherein the magnetized cells are endothelialcells.
 10. A method of repairing a cerebral artery and/or occluding ananeurysm comprising: delivering the stent of any one of claims 1-6 tothe artery such that the portion of the stent comprising the coating isproximal to the aneurysm neck in need of repair and/or occlusion. 11.The method of claim 10, further comprising delivering magnetized cellsto the region of the artery in need of repair.
 12. The method of claim10 or 11, wherein the stent is delivered to the artery in need of repairby catheterization.